1. Field of the Invention
The present invention relates to a capacitance temperature sensor in which temperature is measured by detecting capacitance of a parallel plate condenser which comprises a dielectric material comprising strontium titanate single crystal, and a temperature measuring device using the capacitance temperature sensor.
2. Brief Description of the Background Art
Bulk single crystal strontium titanate (hereinafter referred to as “STO”) is known as a quantum paraelectric material and its dielectric-constant is 20,000 or more at 4.2 K. The dielectric constant of the bulk single crystal strontium titanate depends on bias and stress and decreases according to them.
U.S. Pat. No. 3,649,891 discloses use of a ferroelectric material as a capacitance temperature sensor.
Bulk single crystal STO exhibits a high dielectric constant at low temperatures as mentioned above and thus is an extremely useful dielectric material for superconducting devices or semiconductor devices which are used at low temperatures.
On the other hand, when a ferromagnetic material is used as a capacitance temperature sensor as disclosed in the related art, temperature change causes residual polarization. As a result, hysteresis appears, making it impossible to obtain a capacitance temperature sensor having a one-to-one relationship between the temperature and the capacitance measured.
Further, a capacitance temperature sensor made of a ferroelectric material as disclosed in the related art has been commercialized, but its sensitivity and absolute sensitivity are as low as 20 pF/K and 0.02, respectively. Such a capacitance temperature sensor is thus disadvantageous in that its precision in temperature measurement is low.